The high resolution structure of southern bean mosaic virus (SBMV) has recently been determined in this laboratory. The structure is to be further refined and analyzed in particular with respect to the nature of the quasi-symmetry between protein subunits, in relationship to the amino acid sequence as it becomes available and to the recognition of partially ordered RNA secondary structure. The structure itself, however, has also raised interest into the nature of viral assembly and disassembly. Work has been initiated into the study of swollen particles in the absence of Ca and Mg ions as well as the aggregation of the protein subunits with and without metal ions. The controlling effect of the amino terminal arm is to be studied in the formation of these aggregates, small T equals 1 empty capsids and the crystallization of RNA. A search for factors which bind and might specifically recognize the virus during disassembly has also been started. The effort on the solution of SBMV has created the technology and know-how for the solution of simple virus structures. In addition, the similarity between SBMV and tomato bushy stunt virus, as well as related data, suggests that other spherical plant viruses may be built from adaptations of the same protein fold. Thus it has become imperative to study other simple viruses. It would similarly be of considerable significance to use this new technology in the study of animal viruses to contrast their architectures to those of plant viruses. Hence work is now just starting on the crystallization of various capsids of alfalfa mosaic virus, and it is hoped to reproduce crystals of polio virus and rhino virus. If successful these studies will than lead to complete high resolution determinations.